How to perform the test

Do not electrically disconnect a piezoelectric injector with the engine running. Ensure secure diagnostic electrical connections are made.

Connect the low amp current clamp into PicoScopeChannel A. Set the clamp to the 20 A scale, zero the clamp before connecting to the injector supply circuit.

Start the engine and allow it to idle.

Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture your waveform.

Start the scope to see live data.

Vary the accelerator pedal to see idle, acceleration and overrun injector waveforms.

With your waveforms on screen stop the scope.

Turn off the engine.

Use the Waveform Buffer,Zoom and Measuring tools to examine your waveform.

Note: the orientation of the current clamp relative to the wire will determine whether it has a positive or negative output. If a live waveform does not appear on your screen, or appears to be inverted, try reversing the orientation of the clamp.

Example waveforms

Engine at idle

Increased torque demand

High engine speed

Overrun

Waveform notes

These known good waveforms have the following characteristics:

One or more pairs of positive and negative pulses, which respectively drive the opening and closing of the injector.

The pulses have peak amplitudes around +/- 7 A and cycle from 0 A to their peak value and back within 100 to 200 µs (the precise values will vary with system and test conditions).

Engine idle

3 x pairs of pulses, indicating two pilot injections and one main injection:

The pilot injection durations are around 250 to 350 µs.
The main injection duration is around 450 µs.

Increased torque demand

When the accelerator pedal is depressed and there is a demand for increased engine torque and the main injection duration increases to around 900 µs.

Fast idle speed

With the engine running at a higher speed, the pilot and main injection events all occur within a shorter total time period and their peak currents increase with increased alternator output at higher engine speeds.

Overrun

On engine over-run only the first pilot injection phase remains.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select injector current.

Example piezo injector

Example piezo-stack reaction

Further guidance

A piezoelectric diesel injector delivers atomised fuel directly to the engine combustion chamber when signalled to do so by the Engine Control Module (ECM). The injected fuel quantity is proportional to the injector duration (opening time), fuel rail pressure, fuel temperature and fluid viscosity.

Pilot injection, which delivers a small quantity of diesel prior to the main injection event to better regulate the build-up of combustion pressure and reduce diesel knock; and

Post injection to facilitate exhaust gas treatment processes.

Piezoelectric injectors work using piezo crystal technology:

When pressure is applied to a piezo crystal structure it will produce an electrical current. Conversely when an electrical current is applied to a piezo crystal its structure will change dimensions.

The piezoelectric injector uses these characteristics by having a stack of several hundred wafer thin crystals and applying a current across them. The result is a linear change in stack height which causes a movement of the attached injector needle within the order of microseconds. Once the crystal structure has changed the electrical current does not need to be maintained; the stack will hold its state until an electrical current is applied in the opposite direction.

Diesel injection quantities must be controlled very precisely for accurate emissions control. As such, every individually manufactured or reconditioned injector is tested after assembly and assigned a code that describes its exact injection characteristics. This code must be programmed into the ECM, using a scan tool, whenever an injector is fitted to the engine.

Diagnostically, it is recommended to check the correct injector codes are assigned to the correct cylinders within the ECM if the engine has any misfire, poor performance or excessive emissions symptoms.

Typically, common rail diesel injectors are susceptible to mechanical and electrical faults, producing a variety of symptoms:

Cylinder sealing: if the interface between the injector and the cylinder head is not properly sealed, unburnt or partially burnt gasses and soot can escape from the cylinder during compression and combustion, causing blow-by and reduced cylinder pressures/combustion temperatures, which, in turn, can cause excessive exhaust smoke.

Internal sealing: if an internal seal has failed, fuel will leak from the supply side through to the return side, causing possible high-pressure supply issues, such as a reduced pressure during cranking (where the high-pressure pump speed and its ability to generate sufficient flow is limited).

Electrical circuits: if an injector cannot be energised sufficiently then it’s valve may not open properly, which may cause misfire symptoms.

Contamination: engine or fuel contamination issues may affect the injector outlet, which can affect their flow and spray patterns.

Diagnostic trouble codes

Selection of component-related Diagnostic Trouble Codes (DTCs):

U0105 Lost Communication With Fuel Injector Control Module

U0306 Software Incompatibility with Fuel Injector Control Module

U0406 Invalid Data Received From Fuel Injector Control Module

P0200 - Injector Control Circuit

P0201 - Injector 1 Control Circuit

P0202 - Injector 2 Control Circuit

P0203 - Injector 3 Control Circuit

P0204 - Injector 4 Control Circuit

P0205 - Injector 5 Control Circuit

P0206 - Injector 6 Control Circuit

P0207 - Injector 7 Control Circuit

P0208 - Injector 8 Control Circuit

P0209 - Injector 9 Control Circuit

P0210 - Injector 10 Control Circuit

P0211 - Injector 11 Control Circuit

P0212 - Injector 12 Control Circuit

P0261 - Cylinder 1 Injector Circuit Low

P0262 - Cylinder 1 Injector Circuit High

P0264 - Cylinder 2 Injector Circuit Low

P0265 - Cylinder 2 Injector Circuit High

P0267 - Cylinder 3 Injector Circuit Low

P0268 - Cylinder 3 Injector Circuit High

P0270 - Cylinder 4 Injector Circuit Low

P0271 - Cylinder 4 Injector Circuit High

P0273 - Cylinder 5 Injector Circuit Low

P0274 - Cylinder 5 Injector Circuit High

P0276 - Cylinder 6 Injector Circuit Low

P0277 - Cylinder 6 Injector Circuit High

P0279 - Cylinder 7 Injector Circuit Low

P0280 - Cylinder 7 Injector Circuit High

P0282 - Cylinder 8 Injector Circuit Low

P0283 - Cylinder 8 Injector Circuit High

P0285 - Cylinder 9 Injector Circuit Low

P0286 - Cylinder 9 Injector Circuit High

P0288 - Cylinder 10 Injector Circuit Low

P0289 - Cylinder 10 Injector Circuit High

P0291 - Cylinder 11 Injector Circuit Low

P0292 - Cylinder 11 Injector Circuit High

P0294 - Cylinder 12 Injector Circuit Low

P0295 - Cylinder 12 Injector Circuit High

GT098

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.